1. Field of the Invention
This invention relates to a photomask material and particularly to a photomask material to be used for manufacturing a semiconductor device.
2. Description of the Prior Art
As a mask to be used for manufacturing a semiconductor device, a photograghic emulsion plate formed by a glass substrate was generally utilized in the early days. However, according to the tendency toward high integration with fine patterns, hard masks including a metallic thin film of such as chromium (Cr) formed on a transparent glass substrate are widely utilized these days (for example, see Japanese Patent Laying-Open Gazette No. 157247/1982 or No. 157249/1982).
FIG. 2 is a sectional view of a conventional photomask material. In the figure, a metal film 2 of chromium or the like is formed on a transparent glass substrate 1 of quartz or the like. This metal film 2 of Cr or the like is formed to a thickness of approximately 600 to 800 .ANG. on the transparent glass substrate 1 by an evaporation or sputtering process. In order that a photomask for a semiconductor device may be obtained, photoresist or resist for an electron beam (referred to hereinafter as EB) is coated on the metal film 2 and patterns are formed by irradiation of light or EB, and after that, a developing process and an etching process etc. are applied. If the metal film 2 is formed of Cr, etching is applied by using ceric antimony nitrate and perchloric acid in the case of a wet process or a mixed gas of carbon tetrachloride (CCl.sub.4) and oxygen (O.sub.2) in the case of a dry process. In manufacturing of a mask for a semiconductor device, particularly a highly integrated device having fine patterns such as VLSI, a dry etching process which produces little effect of side etching is preferred.
Although a wet etching process is generally adopted for manufacturing a Cr mask to be used as a mask for manufacturing a conventional semiconductor device, it is difficult in a wet etching process to obtain a mask of high precision due to a side etching effect and the like, while in a dry etching process, the etching speed of Cr is lower than approximately 100 .ANG./min and a ratio of selection of resist is not appropriate and, therefore, the dry etching process is not suited for mass production of photomasks. In addition, in the case of a Cr mask, adhesion to the transparent substrate, particularly the substrate of quartz glass is not good, causing fine patterns to peel off at the time of rinsing the mask.
As means for solving the above stated problems, a method might be considered in which a metal silicide film formed by a silicide transition metal of molybdenum (Mo), tantalum (Ta), tungsten (W) or the like is used as a mask material (for example, see Japanese Patent Application No. 61372/1984). More specifically, silicon (Si) contained in the quartz glass substrate and silicon (Si) contained in the metal silicide film as a mask material are effectively combined to produce strong adhesion. As for etching, dry etching can be easily done (at an etching speed of 1000 .ANG./min) by using mixed gas plasma containing carbon tetrafluoride (CF.sub.4) and oxygen (O.sub.2), compared with the case of a chromium (Cr) mask.
However, the above stated transition metal silicide film has a light reflection factor as high as approximately 50% and as a result, at the time of pattern printing, the resolution of the patterns is decreased due to diverse scattering of light between the wafer and the mask, which makes it difficult to manufacture a VLSI device having submicron patterns.